Induction heat coil arrangement

ABSTRACT

An induction heat coil arrangement, in particular an apparatus for the crucible-free zone melt treatment of a semiconductor rod, including at least two hollow turns with a conduit for guiding a heatexchange fluid contained therein. The outer turn comprises a bent metal tube which is provided with a heat-resistant insulator sleeve to avoid arcings which are detrimental to the induction heat coil arrangement itself as well as to the quality of the semiconductor rod.

[451 Aug. 5, 1975 United States Patent [191 Keller 9 mm Wmm 299 22 "It86 an a nfl ua m nmm uu 08H KBB 244 777 999 NH O45 (O96 I64 7 9 900 v.33

Assignee: Siemens Aktiengesellschaft, Berlin &

Munich, Germany Apr. 12, 1974 FOREIGN PATENTS OR APPLICATIONS 1,230,7265/1971 United Kingdom.............. 219/1079 [22] Filed:

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0pm mm h J ra non n a m nmd mm w wmn (We mm Uta PAS [21] Appl. No.:460,538

[30] Foreign Application Priority Data June 18, 1973Germany......,...................i

[57] ABSTRACT An induction heat coil arrangement, in particular anapparatus for the crucible -free zone melt treatment of ..2l9/10.79;219/1043 Int. Cl. H05b 5/08 a semiconductor rod, including at least twohollow turns with a conduit for guiding a heatexchange fluid containedtherein. The outer turn comprises a bent 2 7 .x O 3 ,2 92 7 v 2 m v 6 334 3 1 1 w m D .1 4 m0 l 7 ms 00 d/ l .w@ F2 00 5 References Cited metaltube which is provided with a heat-resistant in- UNITED STATES PATENTSsulator sleeve to avoid arcings which are detrimental to the inductionheat coil arrangement itself as well as S d. m .e r m u C a n a O r. .mD m 2 e a s S e .m m m f O C y 5 uh m u o e h t O t 393 000 HUN 999 222Stanton...........

Hansen...,......... Keller PATENTEU RUB 51975 HEET 11 INDUQTION HEATCOIL ARRANGEMENT BACKGROUND or THE INVENTION 1 Field of the InventionThe invention generally. relates to induction coil structures and, moreparticularly, to readily producible and easily adjustable inductioncoils which are used in a crucible-free floating melt zone treatment ofsemiconductor rods in a protective gas atmosphere.

2. Prior Art In a crucible-free zone melting process, a semiconductorrod is moved through a melting zone produced by an induction heat coil,in order to improve thedistribution of dopants therein or to transportimpurities to one end of the rod. In addition, this method can be usedto grow monocrystals. It is carried out in a vacuum or in a protectivegas atmosphere consisting of hydrogen, argon ,or another inert gas. Theturns of a coil asdescribed above usually consist of copper or silvertubes, whereby the conduits inside of the tubes are used as passage fora heat-exchange fluid. Electrical energy, usually of a high frequency,is supplied to the coil, to melt the part of the semiconductor-rod whichis encompassed by the coil, while the coil and the rod are slowly movedrelative to one another, so that the material within the rod is treateduniformly.

In the above prior-art arrangements, the current con ducting parts arenot separated from the atmosphere of the melting chamber which usuallyconsists of a protective gas. If a crystal material is desired withoutmolecular dislocations, the zone melting process must be carried out ina very pure protective gas atmosphere at a pressure higher thanatmospheric pressure. In particular, if argon is used as protective gas,and relatively high frequencies are applied, starting approximately at500V, electric arcings may easily occur between the turns of aninduction heat coil, and these arcings have a damaging effect on thequality of the semiconductor crystal. The arcings also damage or destroythe voltage supply lines.

One way of decreasing the possibility of these destructive arcings is byproviding a flat induction heat coil. However, such a coil consumeslarger amounts of current, although the voltage can be decreased. Inaddition, large capacitances are required for tuning its resonance(approximately 24,000pF) due to its low inductivity. It is not possibleto tune lower frequencies since this would require too largecapacitances. In addition, long current paths must be interlaced, due tothe high currents involved.

SUMMARY OF THE INVENTION It is thus an important feature of the presentinvention to produce an induction heat coil wherein arcings areprevented without incurring great cost, even when a relatively highvoltage is used, and to use flat coils while avoiding the disadvantageof a large current consumption.

According to this invention, the coil comprises at least two turns,wherein the outer turn comprises a bent metal tube which is providedwith a heat-resistant insulator sleeve coating and the inner turncomprises a flat coil, which may be grounded.

According to one embodiment of this invention, the outer turn forms apart of the high frequency current supply path, and thevoltage-conducting members are insulated from one another in the areawhere the highest voltage exists. This is particularly important ifsemiconductor rods of relatively large diameters are to be produced orpurified.

According to a further embodiment of the invention, a quartz or glasstube, which is bent in accordance with the-outer turn may be used as aninsulator sleeve, and the outer turn is placed therein.

According to a particularly advantageous embodiment of this invention,the insulator sleeve is formed of ceramic beads which are threaded ontothe metal tube constituting, the outer coil turn whereby the spacesbetween the beads are filled with a temperature-resistant insulatormaterial.

. According to a further embodiment of the invention, the insulatorsleeve is a glass or quartz tissue or cloth soaked or saturated in aninsulator material.

These and other features, objects and advantages of the invention willbecome apparent in the following description thereof, taken inconjunction with the figures of the drawing which illustrate preferredembodiments of a structure manufactures in accordance with theprinciples of the invention.

-BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially sectional topview of a coil structure incorporating the principles of the invention,whereby the outer turn constitutes part of the high frequency currentpath; and

FIG. 2 is a partially sectional top view of an embodiment wherebythe'outer turn isconnected with the high frequencycurrent supply linevia an intermediate metal piece.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates a safetyinduction heating coil for a crucible-free melt zone treatment ofsemiconductor rods in a protective gas atmosphere, in particular anargon atmosphere, consisting of an inner turn I, which is embodied as aflat coil, and a outer turn 2 consisting of an appropriately bent metaltube, such as composed of silver or copper and constituting a part ofthe high frequency current path 3. A sleeve 4 made oftemperature-resistant insulator material is placed over this silver orcopper conductor tube, and extends into the high frequency supply path3. A screw 5A connects coil member l with coil member 2 via theintermediate metal piece 5. Another intermediate metal piece 6 connectsthe coil member I with high frequency current supply path 3. The coilarrangement is sealed by means of silicon rubber seals 7. A protrusion 8may be provided on the inner coil member I for grounding the coilarrangement.

FIG. 2 illustrates a similar embodiment as FIG. l, but here the outerturn 2 does not constitute a part of the high frequency current supplypath but is connected with the current path 3 via an intermediate metalpiece 9. Identical reference numerals have been used in this Figure todenote parts which are similar or identical to those used in FIG. I. Inthis coil arrangement, the outer turn 2 is also provided with a sleeve 4made of a heatresistant electrical insultor material which may beselected from the group consisting of silicon resin, silicon rubber andpolybismaleic imide resin.

The coil arrangement as described above has a greater inductivity than aflat coil with a single winding, and thus the current consumptiondecreases while the voltage increases. An essentially smaller tuningcapacity is required in such an arrangement. As an example, onlyapproximately 6000pF are required for a frequency of 4Ml-lz. Long highfrequency current paths do not need to be interlaced any more, becausethe current is lower and, in addition, the tuning capacitors becomeessentially smaller, even if a low operational frequency is used.

The insulator sleeve 4 preferably consists of ceramic beads which arethreaded onto the outer turn, whereby the spaces between the beads arefilled with a temperature-resistant insulator material which is appliedin a vacuum. This insulator material is preferably silicon rubber,silicon resin or poly bismaleic imide. In another embodiment of theinvention, the insulator sleeve 4 may comprise a quartz or glass clothsaturated or soaked in one of the above insulator materials, forinstance a quartz mantel which is fitted about the outer turn. Further,the insulator sleeve may comprise a quartz or glass tube bent to fitabout the outer turn. The coil turns are preferably made of silver orcopper.

In order to allow the treatment of semiconductor rods with fairly largediameters, the induction heating coil arrangement may be produced as anassembled structure which may be taken apart whereby the coil comprisesof at least two components which are connected with one another byconnections and sealings provided for cooling purposes.

It will be understood that these embodiments of the invention have beendescribed for illustrative purposes only and that various modificationsand variations of the invention may be made without departing from thespirit and scope of the novel concepts thereof.

I claim:

1. An induction heating coil for use in a crucible-free zone meltprocess with an inert gas atmosphere and having at least two turnscomprising:

an outermost turn consisting of a bent metal tube having a peripheralcoating of a heat-resistant electrically insulating material and forminga portion of a high frequency current path; and

an innermost turn comprised of a flat coil.

2. An induction heating coil as defined in claim 1 wherein saidheat-resistant electrically insulating material comprises ceramic beadswhich are threaded over the bent metal tube of the outermost turn.

3. An induction heating coil as defined in claim 2 wherein any spacesbetween said ceramic beads are filled with an insulating material whichis applied in vacuum and is selected from the group consisting ofsilicon resin, silicon rubber and polybismaleic imide resin.

4. An induction heating coil as defined in claim 2 wherein saidperipheral coating comprises a quartz cloth saturated with a materialselected from the group consisting of silicon resin, silicon rubber andpolybismaleic imide resin.

5. An induction heating coil as defined in claim 2 wherein saidheat-resistant electrically insulating material is selected from thegroup consisting of silicon resin, silicon rubber and polybismaleicimide resin.

1. An induction heating coil for use in a crucible-free zone meltprocess with an inert gas atmosphere and having at least two turnscomprising: an outermost turn consisting of a bent metal tube having aperipheral coating of a heat-resistant electrically insulating materialand forming a portion of a high frequency current path; and an innermostturn comprised of a flat coil.
 2. An induction heating coil as definedin claim 1 wherein said heat-resistant electrically insulating materialcomprises ceramic beads which are threaded over the bent metal tube ofthe outermost turn.
 3. An induction heating coil as defined in claim 2wherein any spaces between said ceramic beads are filled with aninsulating material which is applied in vacuum and is selected from thegroup consisting of silicon resin, silicon rubber and polybismaleicimide resin.
 4. An induction heating coil as defined in claim 2 whereinsaid peripheral coating comprises a quartz cloth saturated with amaterial selected from the group consisting of silicon resin, siliconrubber and polybismaleic imide resin.
 5. An induction heating coil asdefined in claim 2 wherein said heat-resistant electrically insulatingmaterial is selected from the group consisting of silicon resin, siliconrubber and polybismaleic imide resin.